With a few exceptions, the more than 75 models of handheld blow dryers that are marketed within the United States today fall into one of two basic categories: the turbo dryer, which is an application of vaneaxial fan, and the professional dryer, which is an application of a centrifugal fan. Of the exceptions, several provide a coverage area of more than 3.5 square inches, and will be discussed separately hereinbelow.
The typical conventional turbo blow dryer is lighter in weight than the typical conventional professional blow dryer, and ranges in weight from 0.50 to 0.75 pound.
The turbo dryer fan design is axial which means the air enters and exits the dryer by traveling along a single axis. This fan includes an impeller usually having four or more blades and and a diameter which is usually less than 1.88 inches. These fans also have, in general, fixed vanes for the impeller to help laminarize the outlet air stream, hence the term vaneaxial fan. The air stream developed by the rotation of the impeller moves longitudinally along the impeller axis of rotation. The cylindrical housing that confines and directs the fan air stream generally has an inside diameter of no more than 1.94 inches. The fractional HP DC motor that drives the impeller is approximately one inch in diameter and is rated upwards of 15,000 RPM.
The electric element used to heat the air stream is nominally rated at 1200 watts with models offered rated at 200 watts to either side of this value. The heating element is functionally supported by wrapping it around the longitudinal axis of a mica frame. The mica frame is made of two pieces that are orthogonally or obliquely fitted together which, when inserted into the heating element duct, forms four quadrants that the air stream is channeled through. The length of the heating element duct is most often a cylindrical match for the fan design, However, some dryers on the market have an elliptical barrel. Regardless of their geometric shape, their heating duct transverse cross-sectional areas range from 1.9 to 2.8 square inches.
In addition to the foregoing features, the typical turbo blow dryer has a pistol style handle with control switches for various heats and air flow rates; an electric power cord nominally 6 feet in length, and possibly a concentrator attachment which may be manually affixed to the outlet port to provide further air stream control for those coiffed styles.
The typical conventional professional dryer ranges in weight from 0.75 to 1.25 pounds and has either a paddle wheel impeller or the centrifugal blower wheel (squirrel cage) impeller.
Both impeller designs draw air in the side of the pistol shaped housing. This air enters at the center of the impeller along its axis of rotation. The rotation of the impeller exerts a centrifugal force on this incoming air causing an air stream to be thrown off radially. The housing confines this radially driven air stream and directs it into the heating element duct. Which is to say, the fan pulls in air from the side of the dryer and changes the air stream direction 90.degree. in order to channel the air into the heating element duct. Either a DC motor, much like that used on the typical turbo dryer motor, or an universal motor is used to drive either type of impeller.
The diameter of the blower wheel impeller starts as low as 2.5 inches and may go up to 6 or more inches. Unfortunately, professional dryers using these larger blower wheels exhibit a moment through the handle. This force is tiring to the user in that it resists any movements by the user that are not exactly in line with the impeller axis of rotation. This moment is a consequence of the mass that rotates about the perimeter of the blower wheel.
Most of the professional dryers, however, use a paddle wheel impeller rather than a blower wheel. The paddle wheel diameters start around 2.5 inches and go up to 5 or more inches. The prevailing trade-off made here is that while the paddle wheel is not as efficient as the blower wheel (and hence is noisier for equivalent CFM), it does not exhibit the moment through the handle that the blower wheel does. In addition, it should be pointed out that the paddle wheel is less costly than the blower wheel.
The electric element used to heat the air stream is nominally rated at 1400 watts with models offered 200 watts above this value and 400 watts below. The heating element duct is generally identical to that of the turbo dryer design, except that not only are the barrels elliptical and circular but they are also rectangular and even trapezoidal. The heating duct cross-sectional areas range from 2 to 3.5 square inches. The additional features that round out the turbo dryer design also finish the design of the typical professional dryer.
Of the conventional dryers which have a relatively large outlet diameter, one has an outlet diameter of approximately 6.125 inches yielding nearly 29.5 squre inches of coverage. This much coverage does not yield effective air stream control or directivity of most hair styles; accordingly, this blow dryer design is aimed at the small-tight-curl hair styles. Correspondingly, its air flow velocity is a slow 170 feet/minute. This air flow velocity does not penetrate to the scalp for most towel dried hair styles and is therefore ineffective from this point of view. The same arguments hold for the Sunbeam model even though its coverage area is slightly scaled. Other models with greater than 3.5 square inches of coverage area tend to be offshoots of the turbo or professional models and they are ineffective for the same reasons the turbo or professional models are.
There are several interrelated disadvantages to the handheld blow dryers of the prior art. The units offered are universally noisy, even to the extent that one winces and dodges when using one. The noise level of the blow dryers is about equivalent to the noise level of vacuum cleaners. These units effectively cover only a small area, approximately the area of the circle created by one's thumb and first finger. Nearly all the conventional blow dryers cause a burning sensation if not kept in constant motion during use. And finally, the air velocity is characteristically so high that it radically displaces the hair during the drying process; this, along with the intense heat, causes the hair to develop small bristly tufts and a ruffled look that is successfuly corrected only with a curling iron.
The Underwriters Laboratory Standard for Electric Personal Grooming Appliances, UL859, establishes that the maximum temperature rise of the outlet air shall not exceed 180.degree. F. Historically, the prior art has elected to market blow dryers with incrementally higher wattages escalating to the present nominal 1200-1400 range. ln order to accommodate these high wattages and meet the UL859 temperature standard, the industry, has been required to increase the air flow rate. This has been done without corresponding alterations to the fan design dimensions or the heating element duct design dimensions. The result of this approach is that the static pressure, the energy loss within the dryer itself, increases quadradically as a function of the air flow rate. This is a direct consequence of the fan laws of physics. As a further result of the fan laws and the fact that the cross-sectional area is not increased, the air flow velocity, i.e. velocity pressure, also increases and is a direct function of the increased flow rate.
These combined deficiencies in the prior art constructional designs place products in the marketplace which are marginally acceptable.